The present disclosure relates to a solid-state imaging device, a method of manufacturing the solid-state imaging device, and an electronic apparatus equipped with a solid-state imaging device, such as a camera.
A CMOS solid-state imaging device or a CCD solid-state imaging device has been proposed as a solid-state imaging device (an image sensor). The solid-state imaging device has been used for a digital camera, a digital video camera, and various portable terminals, such as a camera-mounted mobile phone. The CMOS solid-state imaging device has a power source voltage lower than the CCD solid-state imaging device and is advantageous in view of power consumption.
The CMOS solid-state imaging device has a configuration in which a unit pixel is formed by a photodiode (photoelectric conversion unit) that is a light receiving section and a plurality of pixel transistors and a plurality of pixels are 2-dimensionally arranged. The plurality of pixel transistors is generally composed of four transistors, that is, a transfer transistor, an amplification transistor, a reset transistor, and a selection transistor, or three transistors without the selection transistor. Alternatively, the pixel transistors may be shared by a plurality of diodes. Further, the terminals of the transistors are connected to a multilayered-wire to read out a signal current by applying a desired pulse voltage to the plurality of pixel transistors.
The CCD solid-state imaging device includes a plurality of 2-dimensionally arranged photodiodes that are a light receiving section, vertical transfer resistors having a CCD structure and disposed in the lines of the light receiving sections, respectively, and horizontal transfer resistors having a CCD structure and disposed in the ends of the vertical transfer resistors, and output units of the horizontal transfer resistors.
In the solid-state imaging device, in order to improve the sensitivity characteristic, an on-chip microlens (hereafter, abbreviated as a microlens) on a color filter corresponding to each of the pixels is formed and incident light is condensed to the photodiode by the microlens.
A melt flow process or an etch back process may be used as a method of manufacturing the microlens. The melt flow process is a method of forming a microlens by patterning a material for the microlens which is a photosensitive resistor and performing a reflow process on the material for the microlens formed at each pixel by heat. The etch back process is a method of forming a microlens by forming a lens shape by a photosensitive resistor on a layer of a material for the lens, performing the etch back process in dry etching, and transferring the lens shape onto the material for the lens.
On the other hand, a technology of forming an antireflection coating in a single film or a multi-film on the outer surface of a microlens disposed on a pixel of a solid-state imaging device has been disclosed in Japanese Unexamined Patent Application Publication No. 4-223371. For example, in an antireflection coating implemented by a two-layered film, a first-layer film and a second-layer film are sequentially stacked on the outer surface of the microlens and refraction indexes are set to be lower in order of the first-layer film and the second-layer film from the microlens. That is, the magnitude relationship of the refraction index is microlens>first-layer film>second-layer film. By the configuration of sequentially increasing the refraction index from the second-layer film to the microlens, a change in the refraction index between the air and the microlens becomes small, such that reflection of incident light is prevented. A flare (ghost) caused by reflection is suppressed by the antireflection coating such that the sensitivity characteristic is improved.
A technology of enlarging a lens system and improving a luminosity sensitivity characteristic by forming a microlens cover film that substantially narrows a gap between microlenses on a surface including the microlenses disposed on pixels of a solid-state imaging device has been introduced in Japanese Patent No. 3166199. It is difficult to design the focus of the lens when the difference in refraction index between the microlens and the microlens cover film is large. Therefore, when the refraction index of the microlens is 1.6 to 1.7, it is preferable to use an SiON film having a refraction index of 1.6 to 1.8 as the microlens cover film. On the other hand, it is possible to achieve reduction of chromatic aberration by actively using the difference in refraction index. Further, an antireflection coating may be disposed on the surface of the microlens cover film.